1. Field of the Invention
The present invention relates to a device for recording a signal so as to facilitate effective dropout compensation, and more particularly, to a signal recording device suitable to compensate during playback for a dropout which is generated when a signal is copied in a high-speed dubber of a dual tape deck.
2. The Background Art
Dropout indicates a phenomenon in which noise is generated on a screen by a temporary decrease in the level of, or temporary omission of a playback signal resulting from a partial damage to a recording medium, such as a scratch on a magnetic tape.
A dual tape deck, high-speed dubber, having first and second decks, copies a signal reproduced from a tape of the first deck to a tape of the second deck. When the signal is reproduced in the first deck at a speed N times higher than normal, it is also recorded at a speed N times higher than normal in the second deck. Thus, a high speed dubber can be realized in which dubbing can be performed even at an N-multiple speed. In such a high speed dubber, a luminance signal and a color signal are separately recorded when a signal output from the first deck is recorded to the second deck. A luminance-component FM signal is directly recorded, while only a frequency component of the color signal passed by a low pass filter is recorded.
FIG. 1 is a schematic view of a dropout compensator (DOC) in a general reproducing system. The DOC is comprised of a dropout detector 10, a switching circuit 16, a switch driver 12, and a delay 14 for delaying a signal for one horizontal scanning period.
FIGS. 2A through 2E illustrate the waveforms of signals used to explain the operation of the device of FIG. 1. FIG. 2A illustrates the waveform of an input signal including a dropout. The dropout detector 10 detects a dropout period and generates a gate pulse during the same period as shown in FIG. 2B. The gate pulse shown in FIG. 2B is completely synchronized to coincide with the dropout period of the input signal (see FIG. 2A). The switch driver 12, driven by the gate pulse (see FIG. 2B),activates the switching circuit 16 during the gate pulse period. That is, the switching point of the switching circuit 16 is changed from 16b to 16a during the period the gate pulse is high.
The one horizontal scanning period delay 14 outputs a signal from a previous scan line which has been delayed for one horizontal scanning period (see FIG. 20). Thus, by switching the switching circuit 16 the dropout is compensated to match the signal present before the one horizontal scanning period (see FIG. 2D). The input signal of FIG. 2A is mixed with the compensation signal of FIG. 2D to form a signal free of dropout inducing noise, as shown in FIG. 2E.
FIG. 3 is a block diagram of a conventional signal recording device. The conventional recording device has an input amplifier 200 for amplifying a small signal picked up by a head, a limiter 210 for limiting the signal output from the input amplifier 200 to be within a predetermined amplitude range, and a recording amplifier 220 for amplifying the signal output from the limiter 210.
The operation of the conventional recording device will now be described. A playback signal picked up by the head is amplified in the input amplifier 200, and limited to be within a predetermined amplitude range in the limiter 210. The output signal from the limiter 210 is amplified in the recording amplifier 220. Here, noise components during the dropout period are also amplified in the recording amplifier 220 and recorded on a recording medium.
FIGS. 4A through 4C are a series of waveforms explaining the operation of the signal recording device shown in FIG. 3. FIG. 4A is the waveform of a signal output from the input amplifier 200, showing a dropout signal amplified along with a normal playback signal. FIG. 4B is a signal waveform obtained by limiting the amplitude of the amplified signal to a predetermined level in the limiter 210. From FIG. 4B, it can be seen that limiting the amplitude of the normal playback signal makes it difficult to differentiate the normal playback signal from the dropout signal.
FIG. 4C is a signal waveform recorded as described above and input to a reproducing device. This waveform shows that the dropout period cannot be identified in the input signal. That is, when the input signal is reproduced, the reproducing device treats the dropout signal in the same manner as that for the normal signal without identifying the dropout period. This results in noise appearing on a screen due to a signal recorded during the dropout period.
As described above, in case that a signal is recorded using the conventional recording device, a reproducing device performs a signal reproduction without identifying an original dropout period in the input signal during playback, thereby generating noise due to a signal reproduced during the dropout period.